1. Field of the Invention
The present invention relates to an electret capacitor microphone and particularly to an electret capacitor microphone having an electret capacitor portion, an electrically insulating bush, and a metal cover in which the electret capacitor portion and the electrically insulating bush are stored.
2. Description of the Related Art
Generally, an electret capacitor microphone has an electret capacitor portion including a diaphragm, and a back electrode plate disposed opposite to the diaphragm through a spacer; and an impedance conversion device for converting change of capacitance of the electret capacitor portion into change of electrical impedance.
In most cases, this type electret capacitor microphone is configured so that the electret capacitor portion and an electrically insulating bush for electrically insulating/supporting an outer circumferential edge portion of the back electrode plate are stored in a metal cover, for example, as described in JP-A-11-187494. That is, this type electret capacitor microphone is configured so that the back electrode plate and the metal cover are electrically insulated from each other by the electrically insulating bush.